This invention relates generally to the field of rigid disc drives, and more particularly, but not by way of limitation, to apparatus for improving the capability of a disc drive to withstand the application of mechanical shocks, particularly under non-operational conditions.
Disc drives of the type known as xe2x80x9cWinchesterxe2x80x9d disc drives, or hard disc drives, are well known in the industry. Such disc drives magnetically record digital data on a plurality of circular, concentric data tracks on the surfaces of one or more rigid discs. The discs are typically mounted for rotation on the hub of a brushless DC spindle motor. In disc drives of the current generation, the spindle motor rotates the discs at speeds of up to 10,000 RPM.
Data are recorded to and retrieved from the discs by an array of vertically aligned read/write head assemblies, or heads, which are controllably moved from track to track by an actuator assembly. The read/write head assemblies typically consist of an electromagnetic transducer carried on an air bearing slider. This slider acts in a cooperative hydrodynamic relationship with a thin layer of air dragged along by the spinning discs to fly the head assembly in a closely spaced relationship to the disc surface. In order to maintain the proper flying relationship between the head assemblies and the discs, the head assemblies are attached to and supported by head suspensions or flexures.
The actuator assembly used to move the heads from track to track has assumed many forms historically, with most disc drives of the current generation incorporating an actuator of the type referred to as a rotary voice coil actuator. A typical rotary voice coil actuator consists of a pivot shaft fixedly attached to the disc drive housing base member closely adjacent the outer diameter of the discs. The pivot shaft is mounted such that its central axis is normal to the plane of rotation of the discs. An actuator bearing housing is mounted to the pivot shaft by an arrangement of precision ball bearing assemblies, and supports a flat coil which is suspended in the magnetic field of an array of permanent magnets, which are fixedly mounted to the disc drive housing base member. On the side of the actuator bearing housing opposite to the coil, the actuator bearing housing also typically includes a plurality of vertically aligned, radially extending actuator head mounting arms, to which the head suspensions mentioned above are mounted. When controlled DC current is applied to the coil, a magnetic field is formed surrounding the coil which interacts with the magnetic field of the permanent magnets to rotate the actuator bearing housing, with the attached head suspensions and head assemblies, in accordance with the well-known Lorentz relationship. As the actuator bearing housing rotates, the heads are moved radially across the data tracks along an arcuate path.
Disc drives of the current generation are included in desk-top computer systems for office and home environments, as well as in laptop computers which, because of their portability, can be used wherever they can be transported. Because of this wide range of operating environments, the computer systems, as well as the disc drives incorporated in them, must be capable of reliable operation over a wide range of ambient temperatures.
Furthermore, laptop computers in particular can be expected to be subjected to large amounts of mechanical shock as they are moved about. It is common in the industry, therefore, that disc drives be specified to operate over ambient temperature ranges of from, for instance, xe2x88x925xc2x0 C. to 60xc2x0 C., and further be specified to be capable of withstanding operating mechanical shocks of 100 G or greater without becoming inoperable. Moreover, future disc drive products are being developed which must be capable of withstanding non-operating shocks of up to 1000 G without suffering fatal damage.
One of the undesirable possible consequences of mechanical shocks applied to a disc drive is the phenomenon commonly referred to in the industry as xe2x80x9chead slapxe2x80x9d. This condition occurs when the applied mechanical shock is large enough to overcome the load force applied to the head assembly by the head suspension. Under such conditions, the head assembly lifts away from the disc surface, and when the shock event terminates, the head assembly moves back into contact with the disc in an uncontrolled manner, potentially causing damage to the head assembly, disc or both.
The problems associated with head slap have been exacerbated by the introduction of disc drives including smaller slider assemblies to support the read/write heads, which, by definition, require a smaller amount of applied load force and are, therefore, proportionally more susceptible to uncontrolled unloading due to the application of lesser mechanical shocks. For instance, it is typical for the so-called xe2x80x9c30% sliderxe2x80x9d (0.049xe2x80x3 longxc3x970.039xe2x80x3 widexc3x970.012xe2x80x3 high) to be loaded into cooperative relationship with a disc by a force of only about 4.0 grams. With such a low load force applied to the slider, the amount of applied mechanical shock necessary to cause head slap is also relatively low.
One common preventive measure used in the industry to prevent head slap is to use ramps closely adjacent the outer diameter of the discs to unload the heads from engagement with the discs when a non-operating condition, such as loss of disc drive power, is detected. Since the heads are no longer resting on the disc surface, applied mechanical shocks cannot cause uncontrolled contact between the heads and discs. Once proper operational conditions are restored, the head assemblies are reloaded into engagement with the discs for normal disc drive operation.
Such ramp-loading/unloading schemes, however, typically leave the read/write heads supported only by the delicate gimbal portion of the head suspension during non-operational conditions. In this condition, mechanical shocks applied to the disc drive, if of sufficient magnitude, can result in permanent deformation of the gimbal portion of the head suspension, and potentially fatal damage to the disc drive.
Yet another potentially fatal condition related to applied mechanical shocks relates to the effect of such applied mechanical shocks on the discs themselves. Since the discs are supported only at their inner diameters, mechanical shocks applied in parallel with the spin axis of the discs tend to displace the outer diameters of the discs to positions xe2x80x9cout-of-planexe2x80x9d from the inner diameters of the discs. This phenomenon is often referred to as xe2x80x9cdisc coningxe2x80x9d. Disc coning can result in fatal damage to the disc drive in several modes: 1) if the outer diameters of the discs are axially displaced to an extent great enough to cause contact between the discs and the actuator head mounting arms, particles can be generated within the disc drive which can migrate to the interface between the heads and discs, causing loss of data or fatal damage to the heads, discs or both; 2) if contact between the discs and the actuator head mounting arms due to disc coning is severe enough, this contact can cause the heads to be lifted away from the discs, resulting in head slap, as described above.
A need clearly exists, therefore, for an apparatus for reducing or eliminating head slap in response to applied mechanical shock. It would be a further benefit if the apparatus also acted to minimize the effects of disc coning in response to applied mechanical shock.
The present invention is a head loading ramp structure, located near the inner diameter of the discs of a disc drive, for increasing the load applied to the heads by the head suspension when the heads are moved to a park location near the inner diameter of the discs. In a first embodiment, the ramp structure is stationary and a portion of the disc surface is accessed for normal read/write operations with the increased load applied. In a second embodiment, the ramp structure is moveable and engages the head suspension to increase the load applied to the heads only when the heads are parked during non-operational conditions. The ramp structure optionally includes disc snubber features to reduce disc coning and minimize the axial movement of the ramp structure in response to applied mechanical shocks.
It is an object of the invention to provide a mechanism for increasing the tolerance of a disc drive to applied mechanical shocks.
It is another object of the invention to provide a mechanism for preventing separation of the heads from the discs in a disc drive in response to applied mechanical shocks.
It is another object of the invention to minimize disc coning in a disc drive in response to the application of mechanical shocks.
It is another object of the invention to achieve the previously stated objects in a manner which is simple and economical to implement in a high volume manufacturing environment.
The manner in which these objects are achieved by the present invention, along with other features, benefits and advantages of the invention, can best be understood by a review of the following DETAILED DESCRIPTION OF THE INVENTION, when this is read in conjunction with an examination of the accompanying drawings.